This invention relates to a process for accurately measuring chemical and physical stresses on blood platelets of a human patient and for relating the measured stress to the effect of an outside agent to which the patient is exposed. More particulatly, the present invention relates to such a process and to a kit adapted to effect the stress measurement.
There are approximately 300,000 platelets per cubic mm. blood circulating in the blood stream. Platelets are derived from bone marrow cells and their most dramatic function is to prevent blood loss by forming a plug together with other blood products which stops the flow of blood from an injured vessel. Platelets are induced to aggregate to each other and to adhere to a cut or any foreign surface by metabolites such as ADP, thrombin and epinephrine, as well as by exposed collagen or atherosclerotic plaque in the walls of blood vessels. Changes induced by these agents cause platelets to release substances such as ADP into their immediate surroundings, thus affecting neaby platelets to follow suit. In this way a minor lesion in a blood vessel can accululate platelets and other debris eventually blocking the flow of blood. If the vessel is a coronary artery, the individual experiences a "heart attack". If the vessel is in the brain, a "stroke" results. Very often there is little warning of the impending catastrophy until the vessel is 80-90% occluded and alarming clinical symptoms suddenly become noticeable. Nevertheless, circulating platelets continually pass close to forming clots every two minutes and accumulate information indicative of progressive pathology before any symptoms are felt. Thus, the measurement of early stress reflected in platelets can lead to the institution of highly cost-effective preventative medical therapy to reduce the morbidity and mortality of thrombotic disease. Communicating with stressed platelets before they become irreversibly attached to a clot requires the creative use of technology to decode the internal cell language so that relatively undistorted messages can be registered and correlated with progression of the disease and the effectiveness of treatment.
The platelet like all other living cells uses ATP (adenosine triphosphate) as the most effective source of energy, whereby diverse forms of work can be purchased to maintain the status quo and synthetic output of the cell. ATP itself is made within the cell from simpler compounds such as glucose and amino acids. In the process of supplying energy, ATP is degraded, losing a phosphate group to become ADP (adenosine diphosphate). The process can be repeated forming AMP (adenosine monophosphate). Sustained mild stress of any kind causes the platelet to do more work to maintain itself and, consequently, this is reflected in a shift in the relative amounts of ATP, ADP and AMP, proportional to the degree of stress. With substantial, but not overwhelming stress, AMP is further degraded to HPYX (hypoxanthine). Hypoxanthine is salvageable to some extent to reform AMP which can also be converted back to ADP and hence, to ATP. Overwhelming stress can deplete the platelet of most of its ATP, converting it to a useless circulating body unable to function or causing it to aggregate to other platelets or foreign surfaces.
In addition to being the source of energy in cells, ATP and related compounds do double duty by functioning as conveyers of information to enzymes. Enzymes catalyse the chemical reactions of the cell and are modulated by substances such as ATP, ADP and C-AMP and other molecules and ions in accordance with instantaneous conditions of supply and demand. A disturbance in the communication process, which can occur when ATP/ADP ratios change, or calcium ions are uncontrolled, can lead to an inappropriate wastage of energy stores, a decay of the synchrony between integrated cellular functions and rapid irreversible damage.
The platelet has characteristics of metabolism which enables it to retain evidence of repeated insult in a more permanent fashion than a liver or muscle cell. This capability is due to the fact that the mature platelet, in contrast to other cells, is unable to make ATP from simple molecules, but must constantly recycle its supply of preformed adenine rings to make ATP or scavenge small amounts of circulating ring compounds. Thus, stresses which affect ATP metabolism are not easily or quickly forgotten by the platelet. This memory function is enhanced by the absence of DNA which in other cells is a source of information for repair functions and cell division. Because recycling of ATP and other functions are not totally efficient, normal platelets have a life span of 7-10 days.
A wide variety of outside chemical or physical stresses in the blood system of a human patient can cause the platelet chemistry to change in response to the stress. The condition known as malignant hyperthermia occurs in a small percentage of the population after being exposed to an anesthetic. Malignant hyperthermia is a genetic disorder in which agents such as succinylcholine and halothane can trigger a potentially fatal sequence of events which include acidosis, hyperkalemia, cardiac dysrhythmia, muscle rigidity and hyperthermia. Differences in the order in which symptoms are detected during a malignant hyperthermia episode and the wide variation of their expression at the time of anesthesia makes diagnosis difficult and adds complexity to genetic studies. The range of "triggering" agents has also been enlarged considerably in the light of clinical and experimental observations. Some patients who had previously received significant "triggering" doses of anesthetic without untoward incident, may have a florid malignant hyperthermia episode during subsequent anesthesia. In addition, malignant hyperthermia episodes under conditions of stress have occurred without general anesthesia and with local dental anesthesia. It would be desirable to provide a test to determine whether a patient is susceptible to malignant hyperthermia prior to administration of an anesthetic. Furthermore, it would be highly desirable to provide a means for testing a patient's reaction to physical or chemical stresses in general, including environmental conditions, the effect of drug treatment or the effect of organ or vascular transplant.